The invention relates to a method and a device of manufacturing a continuous material web of elongated fibrous particles from a suspension of the fibrous particles with a concentration at least twice as high as the sediment concentration of the fibrous particles, in which the highly concentrated suspension is distributed and deflected in a chamber before the suspension is passed to a decay channel from which the suspension is deposited.
The industrial paper manufacture has on the whole proceeded in the same way since the beginning of the nineteenth century. Only the machine sizes and the speed of the paper feeding process have increased. The fact that the deckles are bigger and the speeds of the machines have increased has called for all the more accuracy when manufacturing the machine parts. The costs have hence risen greatly and it might be mentioned, that the cost of investment for one modern newsprint machine, including equipment and buildings needed for it, amounts to nearly 35 million dollars. A considerable amount of the costs is needed for its wet end, i.e. the distribution system for the pulp material, inlet box and wire part.
As a principle, by formation of the sheet in a conventional way the following procedure takes place at the wet end of the machine: Fibre suspension, i.e. (more or less freely moving) cellulose fibres in water are roughly distributed over the breadth of the machine in a distribution system, for instance a cross distributor. The purpose of the inlet box is to make the fibres distribute themselves evenly also in micro scale with assistance of the irregular movements (turbulence) of the transporting medium. In order to remedy certain imperfections in the distribution system (for instance involving an oblique speed profile in the inlet box, which besides the fact that this directly results in an uneven surface weight profile across the paper web, it also indirectly results in an unstable flow with rough scale turbulence which appears on the wire section and disturbs the formation of the sheet) a certain number (2-5) perforated cylinders are placed in the way of the flow. The fibres in the suspension have a tendency to agglomerate because of mechanical-geometrical reasons. The perforated cylinders are furthermore supposed to generate turbulent areas of shearing force, meant to break up the fibre flocks occuring. Because of the fibres' tendency to flocculate, which is accentuated in an increased concentration, one cannot maintain a higher fibre concentration than approximately 0.5%, if an acceptable paper is to be had. (0.5 % means 5 g fibres per liter, kg, water).
From the inlet box the suspension, at best with the fibres evenly distributed, is portioned out through a narrow slot, as a horizontal jet, which is allowed to land on the wire (a more or less loose cloth of metal or plastic) which moves at the same speed as the jet. The thickness of the jet can vary from 10 up to or even exceed 50 mm. On the wire most part of the water must be removed. Before all fibres are fixed onto a fibre bed, the concentration must be increased from 0.5 to appr. 10%. With a jet height of 40 mm and an original fibre concentration of 0.5% this consequently means that 40 liters of water must be removed per m.sup.2 of the wire and making use of those machine speeds produced presently by a high speed machine, this must take place within appr. 1 second. The dewatering takes place using various types of dewatering elements, which, depending on the circumstances, may either improve or deteriorate the formation of the sheet. In either case this process is extremely difficult to control.
As the jet lands on the wire the speed of the frame consequently corresponds to that of the jet. The formation of the sheet can therefore principally be compared to a sedimentation process, although an accelerated one, because of the dewatering elements. The sheet will be built up from the under side in such a manner, that the last remaining water has to be drained through practically the whole sheet. The input fibres have a certain size range, which always comprises some fine fractions in which the fibres or actually fibre fragments are so small, that they are washed out together with the water when the draining takes place. The retention, i.e. the part of the fibre material remaining on the wire, often amounts to just 50% or even less. Because of this mechanism one also achieves a sort of two-sided sheet, as here is a certain depletion of material at the bottom of the sheet, while at the same time the contents of such material is higher towards the top face of the sheet. This two-sidedness of the paper will be even more pronounced when some filling substance is added to the beating material, for instance clay in certain qualities of printing paper. This is also characteristic for papers containing wood pulp, i.e. newsprint. The fibre material of such paper contains a high percentage of fine fractions, which results in different printing qualities for the two sides of the sheet. The sheet forming mechanism related above lends the sheet a special two-dimensional structure, when compared to sedimentation. Owing to the geometrical shape (length 1-5 mm, diameter 30-50 .mu.m) all fibres settle in such a way, that they end up in a position parallel to the sheet. The sheet consequently consists of a number of layers parallel to one another, which fact naturally will affect the various qualities of the paper, such as strength, stiffness, etc.
Above related in a simplified way explains the sheet forming process taking place in today's paper manufacture. Other forms, of course, also exist, but they do not to any greater extent differ from the procedure discribed here. The cellulose fibres are in one way or another delivered onto a wire and after the dewatering process has been carried out long enough so that the strength of the sheet formed permits that it be lifted off the wire, it is transported to the press section, where still more water is removed. The final dryness is achieved after the paper has been dried against a number of heated drying cylinders.
In accordance with the U.S. Pat. No. 3,846,230 another manner and an apparatus for forming a continuous pulp path, starting out from a highconcentrated suspension of slim particles, is known. In this case the high concentrated suspension is fed from a cross distributor conforming to accepted standards, through a row of channels connected parallel to one another, the outlet of which taper down to a row of slots, where the pulp is fed on by high speed to a chamber, common for all the channels, where the accelerated flow is lead anew through a throttling for acceleration of the stream, before this is again deflected and fed into a decay channel, in order to decay the turbulence of the flow, before the three dimensional network structure consolidated therein, is deposited. According to this well known technique, a high enough fall of pressure .DELTA.P has to be achieved, over a small enough volume, V, in order to get the power per unit volume needed .epsilon. , whereas the relationship = .epsilon. = .DELTA.PQ/V, where Q means the volume flow. The sediment concentration is hereby defined through the formula C.sub.s = 108 .pi., (l / l).sup.2, when C.sub.s = sediment concentration, r = fibre radius and l = length of fibre.
The object of the present invention is to provide an improvement to the method through which a continuous material path of fibrous particles, outgoing from said suspension of fibrous particles with a concentration corresponding to at least twice the sediment concentration of the fibrous particles can be formed; as well as an improved apparatus by help of which this method can be carried out.